1. Technical Field
This invention relates generally to a fuel system, and more particularly, to a method and apparatus for determining an oil grade of an actuating fluid located within a fuel system.
2. Background Art
In a fuel system having hydraulically-actuated electronically controlled unit injectors (HEUI), high pressure hydraulic actuating fluid flows into a chamber, located within the injector, and pushes down on a plunger which pushes fuel out from a plunger cavity, and out the injector through a nozzle. A solenoid, located within the injector, controls when the high pressure actuating fluid is exposed to the plunger by moving a poppet valve. The amount of fuel injected is controlled by adjusting the duration the solenoid is on.
Engine lubricating oils can be utilized as the hydraulic fluids. There are different types of engine lubricating oils having a variety of grades. The grades range from higher grades, such as 15W40 engine oil, to lower grades, such as 0W20 engine oil. The higher the grade is, the more viscous the oil is.
The viscosity of the actuating fluid effects both the amount of fuel delivered by the injector, and when the delivery process begins. For example, two similar engines, each utilizing a different grade of engine oil, but operating in the same temperature will have different hydraulic fluid viscosities. For example, a first engine utilizing the higher grade engine oil for the actuating fluid is thicker (more viscous) than a second engine utilizing the lower grade engine oil for the actuating fluid. Therefore, on the first engine, when an electrical signal is delivered to a solenoid, commanding the solenoid to deliver actuating fluid to the injector, the fluid flows at a slower rate into the chamber to push against the plunger, than would occur on the second engine. With the actuating fluid moving at a slower rate there is an increased delay before the injector begins delivering fuel. Furthermore, the rate that fuel is delivered depends on the pressure on the plunger. As fuel is delivered the pressure on the plunger will drop unless additional oil is supplied. The first engine is using a more viscous oil and thus the oil will flow more slowly than will be the case for the second engine. This results in a lower actuating pressure and thus lower fuel delivery rate for the first engine. Hence, with the first engine utilizing the high grade engine oil as compared to the second engine utilizing the low grade engine oil, less fuel is delivered by the injectors and the fuel is delivered later in the crank cycle. Under these conditions, unless the oil grade being utilized is determined, overall engine performance is adversely effected, resulting in incomplete combustion, low power, white smoke, etc.
The viscosity of the actuating fluid is a function of the oil grade, the amount the actuating fluid is sheared as the fluid flows through the hydraulic circuit, and the temperature of the actuating fluid. In an operating engine, neither the oil grade, nor the temperature is fixed. For example, a higher grade engine oil or a lower grade engine oil may be used. Also the fuel system operates over a wide range of temperatures, e.g., xe2x88x9250 degrees Fahrenheit through 250 degrees Fahrenheit. The actuating fluid has more viscosity in colder temperatures.
The reduction in fuel delivery and fuel delivery delay increase as the viscosity of the actuating fluid increases. If the different types of oil grades are not accounted for, the fuel delivery and timing may be incorrect making it difficult to start and run the engine especially at high viscosities encountered at cold temperatures. If the fuel delivery is too small the engine may not start or be underpowered. If the fuel delivery is too large the engine structural capabilities may be exceeded, or excessive smoke may be produced. Misfire may occur due to fuel delivery at incorrect (late) ignition timings.
The present invention is directed to overcoming one or more of the problems identified above.
In one aspect of the present invention, a method for determining an oil grade of an actuating fluid located within a fuel system is disclosed. The method includes the steps of determining a temperature of the actuating fluid, a pump speed, a timing event associated with a peak pressure of the actuating fluid, and responsively determining an oil grade of the actuating fluid.
In yet another aspect of the present invention, a method for determining an oil grade of an actuating fluid located within a fuel system is disclosed. The fuel system includes a variable displacement pump having a maximum and minimum displacement position. The method includes the steps of determining a temperature of the actuating fluid, a pump speed, a peak pressure, a rise time of the peak pressure in response to the pump moving from a maximum displacement position to a minimum displacement position, and responsively determining an oil grade of the actuating fluid.
In yet another aspect of the present invention, a method for determining an oil grade of an actuating fluid located within a fuel system is disclosed. The fuel system includes a leakage orifice. The method includes the steps of determining a temperature of the actuating fluid, a pump speed, a peak pressure, a decay time of the peak pressure as a function of the peak pressure and the leakage orifice, and responsively determining an oil grade of the actuating fluid.
In yet another aspect of the present invention, a method for determining an oil grade of an actuating fluid located within a fuel system is disclosed. The method includes the steps of determining a temperature of the actuating fluid, a pump speed, a maximum peak pressure of the actuating fluid, and responsively determining an oil grade of the actuating fluid.
In yet another aspect of the present invention, an apparatus for determining a viscosity range of an actuating fluid located within a fuel system is disclosed. The apparatus includes a pressure sensor adapted to sense a pressure of the actuating fluid, a temperature sensor adapted to sense a temperature of the actuating fluid, and a controller adapted to determine an oil grade of said actuating fluid in response to the pressure and temperature.